Methane conversion process

ABSTRACT

A method for converting methane to higher hydrocarbon products and coproduct water wherein a gas comprising methane and a gaseous oxidant are contacted with a nonacidic catalyst at temperatures within the range of about 700° to 1200° C. A preferred catalyst comprises an alkali component associated with a support material. Results obtained over alkali-promoted solids are enhanced when the contacting is conducted in the presence of halogen promoters.

This is a division of application Ser. No. 06/738,110, filed May 24, 1985.

BACKGROUND OF THE INVENTION

This invention relates to the synthesis of hydrocarbons from a methane source. A particular application of this invention is a method for converting natural gas to more readily transportable material.

A major source of methane is natural gas. Other sources of methane have been considered for fuel supply, e.g., the methane present in coal deposits or formed during mining operations. Relatively small amounts of methane are also produced in various petroleum processes.

The composition of natural gas at the wellhead varies but the major hydrocarbon present is methane. For example, the methane content of natural gas may vary within the range from about 40 to about 95 volume percent. Other constituents of natural gas include ethane, propane, butanes, pentane (and heavier hydrocarbons), hydrogen sulfide, carbon dioxide, helium and nitrogen.

Natural gas is classified as dry or wet depending upon the amount of condensable hydrocarbons contained in it. Condensable hydrocarbons generally comprise C₃ + hydrocarbons although some ethane may be included. Gas conditioning is required to alter the composition of wellhead gas, processing facilities usually being located in or near the production fields. Conventional processing of wellhead natural gas yields processed natural gas containing at least a major amount of methane.

Large scale use of natural gas often requires a sophisticated and extensive pipeline system. Liquefaction has also been employed as a transportation means, but processes for liquefying, transporting, and revaporizing natural gas are complex, energy-intensive and require extensive safety precuations. Transport of natural gas has been a continuing problem in the exploitation of natural gas resources. It would be extremely valuable to be able to convert methane (e.g., natural gas) to more readily handleable or transportable products. Moreover, direct conversion to olefins such as ethylene or propylene would be extremely valuable to the chemical industry.

U.S. Pat. No. 4,199,533 discloses a process for converting methane to higher molecular weight hydrocarbons by using chlorine gas as a recyclable catalyst. The process produces ethylene as a major product along with hydrogen chloride, which is converted to chlorine for recycle in the system. Major drawbacks of the '533 process are the large amount of chlorine required, the necessity of regenerating chlorine from hydrogen chloride to maintain an economically viable system, and the need to use operating temperatures in excess of 1000° C. to produce ethylene.

Recently, it has been discovered that methane may be converted to higher hydrocarbons (e.g., ethane, ethylene and higher homologs) with minimal formation of carbon oxides by contacting methane with a reducible metal oxide as a selective oxygen source. As the methane is converted to hydrocarbon products and coproduct water, the active oxygen of the metal oxide is depleted, resulting in a reduced metal oxide. The reduced metal oxide is relatively inactive for the oxidative conversion of methane but active oxygen may be replaced by regeneration of a reducible metal oxide. Such regeneration is accomplished by reoxidation of the reduced metal oxide.

Reducible oxides of several metals have been identified which are capable of converting methane to higher hydrocarbons. Oxides of manganese, tin, indium, germanium, lead, antimony and bismuth are particularly useful. See U.S. Pat. Nos. 4,443,649; 4,444,984; 4,443,648; 4,443,645; 4,443,647; 4,443,644; and 4,443,646. Also see U.S. Pat. Nos. 4,499,323 and 4,499,324.

U.S. Pat. No. 4,499,322 discloses and claims a process for the conversion of methane to higher hydrocarbon which comprises contacting methane with an oxidative synthesizing agent containing a promoting amount of alkali metal and/or compounds thereof.

U.S. Pat. No. 4,495,374 discloses and claims a process for the conversion of methane to higher hydrocarbons which comprises contacting methane with an oxidative synthesizing agent containing a promoting amount of alkaline earth metal and/or compounds thereof.

Hinsen and Baerns report studies of a continuous mode for the oxidative coupling of methane wherein regenerating air is cofed with the methane feed. Hinsen, W. and Baerns, M., "Oxidative Koppling von Methan zu C₂ -Kohlenwasserstoffen in Gegenwart unterschiedlicher Katalysatoren", Chemiker-Zeitung, Vol. 107, No. 718, pp. 223-226 (1983). Using a catalyst based on lead oxide and gamma-alumina in a fixed bed reactor operated at 1 atmosphere total pressure and 600°-750° C., they report results of approximately 53% selectivity to ethane and ethylene at 8% methane conversion for a feed consisting of about 50% methane, 25% air and 25% nitrogen. Other metal oxides studies by Hinsen and Baerns included oxides of Bi, Sb, Sn and Mn.

Commonly-assigned U.S. patent application Ser. No. 600,656, filed Apr. 16, 1984, discloses and claims a process for converting methane to higher hydrocarbons which comprises contacting methane and an oxygen-containing gas with a solid comprising a reducible metal oxide and an alkali/alkaline earth metal promoter.

Commonly-assigned U.S. patent application Ser. No. 600,670, filed Apr. 16, 1984, discloses and claims a process for converting methane to higher hydrocarbons which comprises contacting methane and an oxygen-containing gas with a manganese silicate.

Oxidative condensation of methane in the presence of solid superacid catalysts is disclosed in U.S. Pat. Nos. 4,433,192; 4,465,893; and 4,467,130. European Published Patent Application 93,543 discloses a process for aromatizing methane wherein a methane feedstock and an oxidizing agent other than molecular oxygen are contacted at temperatures of about 10° to 600° C. with a solid acidic catalyst having Bronsted acid sites.

The reaction products of such processes are hydrocarbons, carbon oxides, coke and water. It would be beneficial in these processes to reduce selectivities to carbon oxides and coke and to increase methane conversions to the desired hydrocarbon products. Accordingly, an object of this invention is to provide an improved process for converting methane to higher hydrocarbons. More particular aspects, objects and the several advantages of this invention will become apparent to those skilled in the art upon reading this disclosure and the appended claims.

SUMMARY OF THE INVENTION

It has now been found that methane may be converted to higher hydrocarbons by contacting a gas comprising methane and a gaseous oxidant with a nonacidic solid catalyst at a temperature within the range of about 700° to 1200° C. The gaseous oxidant is selected from the group consisting of oxygen, oxygen-containing gases and oxides of nitrogen. Preferably, solids employed are low surface area solids-solids having surface areas less than about 50 cm² /gram, more preferably solids having surface areas within the range of about 0.1-10 m² /gram. A further desired characteristic of the solid employed in this invention is that the solid is substantially nonreducible under process conditions. While a characteristic of the present process is coproduction of water, the present process does not require the presence of reducible metal oxides.

In a distinct, second aspect of this invention, methane and a gaseous oxidant are contacted with a catalyst comprising an alkali metal component associated with a support material at a temperature within the range of about 700° to 1200° C. The alkali metal component is selected from the group consisting of Li, Na, K, Rb, and Cs and compounds thereof. Lithium, sodium and compounds thereof are preferred alkali metal components. The support material is preferably a nonacidic solid. Again, the surface area of the composited catalyst is preferably less than about 50 cm² /gram, more preferably within the range of about 0.1-10 m² /gm. And again, desired catalysts are substantially nonreducible under process conditions.

In a distinct, third aspect of this invention, methane and a gaseous oxidant are contacted with a catalyst comprising an alkali metal component associated with a support material at a temperature within the range of about 700°-1200° C. and in the presence of a promoter selected from the group consisting of halogens and compounds thereof. The promoter may be incorporated into the catalyst prior to conducting the contacting, but preferably the promoter is at least periodically introduced with methane and the gaseous oxidant while conducting the contacting. Halogens are selected from the group consisting of Fl, Cl, Br and I. Presently preferred halogen promoters are chlorine, bromine and compounds thereof. Chlorine and compounds of chlorine are particularly preferred.

The catalytic process of this invention offers the advantage of employing simpler, less complex solid systems than those processes, described above, which employ solids comprising reducible metal oxides. Moreover, use of the nonacidic catalysts of the present invention minimizes the coking and product decomposition problems encountered with acidic catalyst systems,

DETAILED DESCRIPTION OF THE INVENTION

In addition to methane the hydrocarbon feedstock employed in the method of this invention may contain other hydrocarbon or non-hydrocarbon components. The methane content of the feedstock, however, will typically be within the range of about 40 to 100 vol. %, preferably within the range of about 80 to 100 vol. %, more preferably within the range of about 90 to 100 vol. %.

The gaseous oxidant is selected from the group consisting of molecular oxygen, oxides of nitrogen, and mixtures thereof. Preferably, the gaseous oxidant is an oxygen-containing gas. A preferred oxygen-containing gas is air. Suitable oxides of nitrogen include N₂ O, NO, N₂ O₃, N₂ O₅ and NO₂. Nitrous oxide (N₂ O) is a presently preferred oxide of nitrogen.

The ratio of hydrocarbon feedstock to gaseous oxidant gas is not narrowly critical to the present invention. However, the ratio will desirably be controlled to avoid the formation of gaseous mixtures within the flammable region. The volume ratio of hydrocarbon/gaseous oxidant is preferably within the range of about 0.1-100:1, more preferably within the range of about 1-50:1. Methane/gaseous oxidant feed mixtures containing about 50 to 90 volume % methane have been found to comprise a desirable feedstream.

The solid employed in this invention is generally characterized as "nonacidic". This descriptor is meant to refer to the main, predominant surface properties of the solids. For example some solid bases are known to have acidic properties to some extent. See Tanabe, K., "Solid Acid and Base Catalysts." In: Catalysis Science & Technology, vol. 2 (New York, Springer-Verlag Berlin Heidelberg, 1981). Currently preferred solids used in the present process are characterized by negligible acidity (less than about 0.01 meq/gm) in the H_(o), range less than about 3.3, preferably less than about 6.8. H_(o) is the Hammett acidity parameter described on pp. 234-241 of Tanabe.

A futher characteristic of preferred solids for the present process is a relatively low surface area. Solids having surface areas less than about 50 cm² /gm are suitable, but the surface areas of preferred solids are within the range of about 0.1.-10 m² /gm.

A still further characteristic of preferred solids for the present process is that they be stable and substantially nonreducible under process conditions. Examples of suitable solids include those solid bases described in Table 2 on p. 233 of Tanabe, supra. However, presently preferred solids are metal oxides and mixed oxides. Alkaline earth oxides are particularly preferred, especially MgO and CaO. Other suitable metal oxides are SiO₂, alpha-Al₂ O₃, La₂ O₃, ThO₂, TiO₂, and ZrO₂. Such materials are relatively stable under the conditions of the present process.

One preferred solid employed in the present process comprises an alkali metal component associated with a support material. Preferred support materials are those nonacidic solids described above. Alkali metals are selected from the group consisting of Li, Na, K, Rb and Cs. Preferred components are Li, Na and compounds thereof. The wt. % loading of the alkali metal component (expressed as wt. % alkali metal in composite) is preferably within the range of about 0.01 to 99 wt. %, more preferably within the range of about 0.1 to 10 wt. %.

Phosphorus components may also be added to the solid. Again, the amount contained in the solid is not narrowly critical.

Composite solids can be prepared by any suitable method. For example, alkali-promoted solids may be prepared such methods as adsorption, impregnation, precipitation, coprecipitation and dry mixing. When phosphorus is incorporated into the catalyst, it is desirably provided in the form of a phosphate of an alkali metal.

A suitable method of preparation is to impregnate a support with solutions of the desired metals. Suitable compounds useful for impregnation include the acetates, acetylacetonates, oxides, carbides, carbonates, hydroxides, formates, oxalates, nitrates, phosphates, sulfates, sulfides, tartrates, fluorides, chlorides, bromides, or iodides. After impregnation the preparation is dried to remove solvent and the dried solid is calcined, preferably in air, at a temperature within the range of about 300° to 1200° C. Particular calcination temperatures will vary depending upon the particular metal compound or compounds employed.

In one preferred embodiment of this invention, a gas comprising methane and a gaseous oxidant are contacted with a catalyst comprising an alkali metal component associated with a support material in the presence of a promoter selected from the group consisting of halogens and compounds thereof. Halogens are selected from the group consisting of F, Cl, Br and I. Preferred promoters are Cl, Br, and compounds thereof. Chlorine-containing promoters are particularly preferred.

Halogen promoters are preferably introduced into the process with gaseous feedstreams flowing to the process. Any suitable concentration of promoter can be used. The promoter can be introduced continuously or periodically, although continuous introduction is preferred. Suitable sources of halogen include free halogen gas, hydrogen halides, ammonium halides, aliphatic halides (e.g., methyl halide, methylene halide, ethyl halide, amyl halide, allyl halide), cycloaliphatic halides (e.g., cyclohexyl halide), halogen substituted aliphatic acids such as methyl amine hydrochloride, and the like. Mixtures of various halogen sources may be used. Presently preferred are free halogen gas, aliphatic halides and hydrogen halides. Methane/gaseous oxidant feed mixtures containing about 0.01 to 10 vol. % halogen promoter, preferably about 0.1 to 5 vol. %, are desirable feedstreams.

Preferably, methane and oxygen are contacted with the agent in the substantial absence of catalytically effective nickel, noble metals and compounds thereof. (i.e., nickel, rhodium, palladium, silver, osmium, iridium, platinum and gold) to minimize the deleterious catalytic effects thereof. These metals, when contacted with methane at the temperatures employed in the first step of the present invention, tend to promote coke formation, and the metal oxides tend to promote the formation of combustion products rather than the desired hydrocarbons. The term "catalytically effective" is used herein to identify that quantity of one or more of nickel and of the noble metals and compounds thereof which substantially changes the distribution of products obtained in the method of this invention relative to such contacting in the absence of such metals and compounds thereof.

Operating temperatures for the method of this invention are generally within the range of about 700° to 1200° C., more preferably within the range of about 800° to 1000° C.

Operating pressures are not critical to the presently claimed invention. However, both general system pressure and partial pressures of methane and oxygen have been found to effect overall results. Preferred operating pressures are within the range of about 0.1 to 30 atmospheres.

The space velocity of the gaseous reaction streams are similarly not critical to the presently claimed invention, but have been found to effect overall results. Preferred total gas hourly space velocities are within the range of about 10 to 100,000 hr.⁻¹, more preferably within the range of about 600 to 40,000 hr.⁻¹.

The catalyst may be maintained in the contact zone as fixed, moving, or fluidized beds of solids. A fixed bed of solids is currently preferred for the method of this invention.

The effluent from the contact zone contains higher hydrocarbon products (e.g., ethylene, ethane and other light hydrocarbons), carbon oxides, water, unreacted hydrocarbon (e.g., methane) and oxygen, and other gases present in the oxygen-containing gas fed to the contact zone. Higher hydrocarbons may be recovered from the effluent and, if desired, subjected to further processing using techniques known to those skilled in the art. Unreacted methane may be recovered and recycled to the contact zone.

The invention is further illustrated by reference to the following examples. Experimental results reported below include conversions and selectivities calculated on a carbon mole basis.

EXAMPLE 1

A gaseous feedstream consisting of 50 vol. % air in methane was contacted with MgO and the results shown in Table I were obtained.

                  TABLE 1                                                          ______________________________________                                         CH.sub.4 /Air Over MgO                                                                  CH.sub.4                                                              Temp.    GHSV          % CH.sub.4                                                                             % C.sub.2 +                                     (°C.)                                                                            (hr..sup.-1)  Conv.   Sel.                                            ______________________________________                                         700      2400          14.8    29.2                                            700      4800          10.2    33.3                                            750      2400          20.8    49.0                                            750      2400          16.2    43.7                                            775      2400          16.0    33.1                                            800      4800          14.7    31.9                                            825      2400          16.9    42.2                                            900      2400          20.6    48.9                                            900      4800          19.9    55.2                                            ______________________________________                                    

EXAMPLE 2

A gaseous feedstream consisting of methane and air was contacted with a solid consisting of 0.36 wt. % Li on MgO and the results shown in Table 2 were obtained.

                                      TABLE 2                                      __________________________________________________________________________     CH.sub.4 /Air Over 0.36% Li/MgO                                                Vol %                                                                          Air                                                                            in  Temp                                                                               CH.sub.4                                                                           % Conv.                                                                               % Selectivity to:                                           CH.sub.4                                                                           (°C.)                                                                       GHSV                                                                               CH.sub.4                                                                          O.sub.2                                                                            C.sub.2 =                                                                          C.sub.2                                                                            C.sub.2 +                                                                          CO  CO.sub.2                                    __________________________________________________________________________     10  700 1200                                                                               0.5                                                                                4  15  82  97  0    2                                          10  800 1200                                                                               3.0                                                                               56  53  37  98  0    2                                          10  900 1200                                                                               5.3                                                                               87   6   8  18  81.9                                                                                0                                          30  800 1200                                                                               10.0                                                                              75  48  17  72  22   6                                          30  900 1200                                                                               14.4                                                                              85  14   1  16  75   9                                          50  700 1200                                                                               7.8                                                                               41  12  26  39  0   61                                          50  750 1200                                                                               16.5                                                                              80  26  22  51  7   42                                          50  800 1200                                                                               20.2                                                                              92  35  24  63  0   37                                          50  825 1200                                                                               22.1                                                                              93  38  20  64  5   31                                          50  900 1200                                                                               21.4                                                                              93  42   7  57  11  32                                          50  825 2400                                                                               21.0                                                                              81  37  19  60  15  25                                          50  900 2400                                                                               23.3                                                                              93  44  16  67  10  23                                          50  925 2400                                                                               23.3                                                                              93  46  13  66  11  23                                          50  825 4800                                                                               11.9                                                                              38  30  30  63  15  22                                          50  900 4800                                                                               23.6                                                                              83  42  19  65  17  18                                          50  925 4800                                                                               24.6                                                                              N/A 44  17  66  17  17                                          __________________________________________________________________________

EXAMPLE 3

A gaseous feedstream consisting of 50 vol. % air in methane and containing 0,76 vol, % CH₃ Cl was contacted with a solid consisting of 0.36 wt. % Li on MgO and the results shown in Table 3 were obtained, The CH₄ GHSV was 2400 hr, ⁻¹.

                  TABLE 3                                                          ______________________________________                                         CH.sub.4 /Air/CH.sub.3 Cl Over 0.36% Li/Mgo                                    Temp   % CH.sub.4                                                                              % Selectivity to:                                              (°C.)                                                                          Conv.    C.sub.2 =                                                                              C.sub.2                                                                              C.sub.2 +                                                                            CO    CO.sub.2                             ______________________________________                                         775    14.3     49.6    13.9  67.7  25.4  4.9                                  825    25.4     48.4     6.0  59.5  34.0  6.5                                  ______________________________________                                    

EXAMPLE 4

A gaseous feedstream consisting of 50 vol. % air in methane and containing varying amounts of HCl was contacted with a solid consisting of 0.36 wt. % Li on MgO and the results shown in Table 4 were obtained.

                  TABLE 4                                                          ______________________________________                                         CH.sub.4 /Air/HCl over 0.36% Li/MgO                                            Vol. %          CH.sub.4                                                       HCl in Temp.    GHSV     % CH.sub.4                                                                            % C.sub.2 +                                    Feed   (°C.)                                                                            (hr..sup.-1)                                                                            Conv.  Selectivity                                                                            C.sub.2 =/C.sub.2                      ______________________________________                                         0      775      2400     <1%    >90%    --                                     0.05   775      2400     13.4   55.7    1.39                                   0.5    775      2400     20.9   74.1    4.32                                   1.0    775      2400     21.4   64.4    7.17                                   0      825      2400     21.0   60.2    1.99                                   0.05   825      2400     23.8   61.7    2.79                                   0.5    825      2400     29.9   68.7    7.28                                   1.0    825      2400     28.7   69.5    8.85                                   0      900      2400     23.3   67.7    2.71                                   0.05   900      2400     27.6   65.0    3.81                                   0.5    900      2400     31.6   73.3    9.59                                   1.0    900      2400     31.1   72.8    13.85                                  0      800      4800     <1%    --      --                                     0.05   800      4800     12.2   67.2    1.09                                   0.5    800      4800     20.7   72.8    3.51                                   1.0    800      4800     15.2   73.5    4.56                                   0      900      4800     23.6   65.0    2.25                                   0.05   900      4800     28.2   68.6    3.13                                   0.5    900      4800     32.2   72.6    8.17                                   1.0    900      4800     33.6   69.6    10.25                                  ______________________________________                                    

EXAMPLE 5

A gaseous feedstream consisting of 50 vol. % air in methane was contacted with a solid consisting of 5 wt. % Li on MgO and the results shown in Table 5 were obtained.

                  TABLE 5                                                          ______________________________________                                         CH.sub.4 /Air Over 5% Li/MgO                                                   Temp  CH.sub.4 % CH.sub.4                                                                             % Selectivity to:                                       (°C.)                                                                         GHSV     Conv.   C.sub.2 =                                                                            C.sub.2                                                                             C.sub.2 +                                                                            CO   CO.sub.2                          ______________________________________                                         800   2400     11.3    39.9  23.7 67.7  18.2 14.6                              825   2400     16.0    41.9  14.9 60.4  24.5 15.1                              900   2400     22.5    47.9   7.2 59.9  16.6 23.6                              925   2400     22.8    48.8   6.1 61.1  13.3 25.6                              825   4800      9.2    37.4  31.4 72.5  14.6 13.0                              900   4800     19.6    46.1  13.1 60.7  21.9 17.5                              925   4800     22.1    46.7  11.0 62.5  18.3 19.2                              925   9600     15.3    44.3  15.9 64.5  22.1 13.3                              ______________________________________                                    

EXAMPLE 6

A gaseous feedstream consisting of varying amounts of air in methane was contacted with a solid consisting of 1.2 wt. % Na on MgO and the results shown in Table 6 were obtained.

                                      TABLE 6                                      __________________________________________________________________________     CH.sub.4 /Air over Na/Mgo                                                      % Air                                                                          in  Temp CH.sub.4                                                                           % Conv.                                                                               % Selectivity to:                                          CH.sub.4                                                                           (°C.)                                                                        GHSV                                                                               CH.sub.4                                                                           O.sub.2                                                                           C.sub.2 =                                                                          C.sub.2                                                                           C.sub.2 +                                                                          CO  CO.sub.2                                    __________________________________________________________________________     10  700  1200                                                                               1.4 31 14.7                                                                               69.6                                                                              85.6                                                                               0   14.4                                        10  825  1200                                                                               8.3 89 23.2                                                                               17.5                                                                              42.0                                                                               58.1                                                                               0                                           10  900  1200                                                                               7.5 90 20.9                                                                                9.9                                                                              36.8                                                                               63.2                                                                               0                                           30  700  1200                                                                               3.4 39  5.3                                                                               25.0                                                                              30.6                                                                               23.5                                                                               45.9                                        30  825  1200                                                                               10.2                                                                               93 38.5                                                                               31.0                                                                              74.3                                                                               0   25.7                                        30  900  1200                                                                               11.3                                                                               92 52.8                                                                               11.8                                                                              74.4                                                                               5.5 20.1                                        50  800  1200                                                                               16.6                                                                               83 23.8                                                                               19.5                                                                              44.1                                                                               12.9                                                                               43.0                                        50  900  1200                                                                               21.9                                                                               93 40.0                                                                               17.6                                                                              62.5                                                                               6.0 31.6                                        50  800  1200                                                                               11.9                                                                               54 18.4                                                                               24.1                                                                              43.8                                                                               19.1                                                                               37.0                                        50  900  2400                                                                               21.5                                                                               93 36.8                                                                               21.5                                                                              62.7                                                                               7.4 29.9                                        50  825  4800                                                                               9.1 29 22.2                                                                               28.2                                                                              51.4                                                                               19.5                                                                               29.1                                        50  900  4800                                                                               16.2                                                                               64 32.3                                                                               25.7                                                                              60.6                                                                               14.5                                                                               24.9                                        __________________________________________________________________________

EXAMPLE 7

A gaseous feedstream consisting of 50 vol. % air in methane was contacted with a solid consisting of 2 wt. % K on MgO and the results shown in Table 6 were obtained.

                  TABLE 7                                                          ______________________________________                                         CH.sub.4 /Air Over K/MgO                                                             CH.sub.4                                                                 Temp  GHSV     % CH.sub.4                                                                             % Selectivity to:                                       (°C.)                                                                         (hr..sup.-1)                                                                            Conv.   C.sub.2 =                                                                            C.sub.2                                                                             C.sub.2 +                                                                            CO   CO.sub.2                          ______________________________________                                         700   1200     6.6     0      3.8  3.8  32.0 64.3                              800   1200     14.0    10.8  12.3 23.6  16.9 59.7                              900   1200     18.1    32.7   5.5 42.6  16.3 41.1                              900   2400     19.3    32.2  14.5 49.9  14.9 35.2                              925   2400     20.0    37.0  10.8 52.6  13.7 33.7                              925   4800     17.5    37.4  12.1 53.5  29.3 17.3                              925   9600     9.3     34.3  19.7 60.7  31.5  7.8                              ______________________________________                                    

EXAMPLE 8

A gaseous feedstream consisting of varying amounts of N₂ O in methane was contacted with a solid consisting of 2 wt. % Na on MgO and the results shown in Table 8 were obtained. The CH₄ CHSV was 900 hr.⁻¹.

                  TABLE 8                                                          ______________________________________                                         CH.sub.4 /NgO Over Na/MgO                                                      Vol %                                                                          N.sub.2 O                                                                            Initial                                                                  in    Temp    % CH.sub.4                                                                             % Selectivity to:                                        CH.sub.4                                                                             (°C.)                                                                           Conv.   C.sub.2 =                                                                            C.sub.2                                                                              C.sub.2 +                                                                            CO   CO.sub.2                          ______________________________________                                         10    700     0.5     0     100   100   0    0                                 10    750     1.8     23.5  74.4  100   0    0                                 10    800     5.6     48.4  36.8  94.9  2.6  2.5                               10    825     8.0     53.0  22.8  90.5  4.2  5.3                               30    700     1.0     0     99.9  99.9  0    0                                 30    750     4.0     25.9  63.6  93.3  4.3  2.3                               30    800     11.3    47.0  26.1  83.5  8.4  8.0                               30    825     17.3    48.7  15.0  75.7  10.0 14.4                              ______________________________________                                    

EXAMPLE 9

A gaseous feedstream consisting of 50 vol. % air in methane was contacted with a SiO₂ at varying CH₄ GHSV and the results shown in Table 9 were obtained. The initial temperature of each run was 800° C.

                  TABLE 9                                                          ______________________________________                                         CH.sub.4 /Air Over SiO.sub.2                                                   CH.sub.4                                                                       GHSV   % CH.sub.4                                                                              % Selectivity to:                                              (hr..sup.-1)                                                                          Conv.    C.sub.2 =                                                                              C.sub.2                                                                              C.sub.2 +                                                                            CO    CO.sub.2                             ______________________________________                                          600   14.4     13.8    5.2   19.7  46.4  33.9                                 1200   14.1     11.4    7.1   19.2  48.4  32.4                                 2400   14.0     12.1    9.6   22.4  48.2  29.3                                 4800   14.4     13.8    11.8  26.3  47.4  26.3                                 ______________________________________                                    

EXAMPLE 10

A gaseous feedstream consisting of varying amounts of air in methane was contacted with a solid consisting of 1 wt. % Na on SiO₂ and the results shown in Table 10 were obtained.

                                      TABLE 10                                     __________________________________________________________________________     CH.sub.4 /Air Over Na/SiO.sub.2                                                Vol %                                                                          Air                                                                            in  Temp                                                                               CH.sub.4                                                                           % Conv.                                                                               % Selectivity to:                                           CH.sub.4                                                                           (°C.)                                                                       GHSV                                                                               CH.sub.4                                                                          O.sub.2                                                                            C.sub.2 =                                                                          C.sub.2                                                                            C.sub.2 +                                                                          CO  CO.sub.2                                    __________________________________________________________________________     10  700 1200                                                                               0.1                                                                               7   14.9                                                                               85.1                                                                               100 0   0                                           10  800 1200                                                                               0.8                                                                               32  29.9                                                                               64.4                                                                               95.9                                                                               0   4.1                                         10  900 1200                                                                               2.9                                                                               90  59.5                                                                               17.5                                                                               95.2                                                                               0   4.8                                         30  700 1200                                                                               0.1                                                                               2   14.8                                                                               85.2                                                                               100 0   0                                           30  800 1200                                                                               2.5                                                                               18  14.7                                                                               27.5                                                                               43.0                                                                               51.7                                                                               5.3                                         30  900 1200                                                                               9.1                                                                               89  39.4                                                                               10.9                                                                               61.3                                                                               29.5                                                                               9.3                                         50  700 1200                                                                               0.1                                                                               0.5 11.5                                                                               66.9                                                                               78.4                                                                               0   21.6                                        50  800 1200                                                                               2.8                                                                               10  11.5                                                                               27.7                                                                               39.7                                                                               53.6                                                                               39.7                                        50  900 1200                                                                               15.1                                                                              N/A 31.3                                                                               10.3                                                                               46.2                                                                               44.1                                                                               46.2                                        50  800 2400                                                                               1.0                                                                               7   23.9                                                                               65.6                                                                               90.5                                                                               0   9.5                                         50  900 2400                                                                               13.4                                                                              54  30.1                                                                               11.0                                                                               45.1                                                                               48.5                                                                               6.4                                         50  925 2400                                                                               15.8                                                                              71  31.3                                                                                7.8                                                                               43.9                                                                               47.9                                                                               8.2                                         __________________________________________________________________________

EXAMPLE 11

A gaseous feedstream consisting of 50 vol, % air in methane was contacted with a solid consisting of 0.29 wt. % Li on SiO₂ and the results shown in Table 11 were obtained.

                  TABLE 11                                                         ______________________________________                                         CH.sub.4 /Air Over Li/SiO.sub.2                                                Temp  CH.sub.4                                                                               % CH.sub.4                                                                             % Selectivity to:                                        (°C.)                                                                         GHSV    Conv.   C.sub.2 =                                                                            C.sub.2                                                                              C.sub.2 +                                                                            CO    CO.sub.2                         ______________________________________                                         825   1200    10.5    24.8  13.0  40.2  51.4  8.4                              900   1200    18.0    28.9   3.9  40.4  49.1  10.5                             900   2400    14.2    30.2   9.0  42.6  51.8  5.6                              925   2400    16.3    30.8  6.21  40.8  53.1  6.1                              ______________________________________                                    

EXAMPLE 12

A gaseous feedstream consisting of varying amounts of N₂ O in methane was contacted with a solid consisting of 5 wt. % NaP₂ O₇ on SiO₂ and the results shown in Table 12 were obtained. The CH₄ GHSV for each run was 900 hr.⁻¹.

                  TABLE 12                                                         ______________________________________                                         CH.sub.4 /N.sub.2 O Over Na.sub.4 P.sub.2 O.sub.7 /SiO.sub.2                   Vol %                                                                          N.sub.2 O                                                                            Initial                                                                  in    Temp     % CH.sub.4                                                                             % Selectivity to:                                       CH.sub.4                                                                             (°C.)                                                                            Conv.   C.sub.2 =                                                                            C.sub.2                                                                             C.sub.2 +                                                                            CO   CO.sub.2                          ______________________________________                                         10    750      5.0     33.2  40.7 80.7  14.9 4.0                               10    800      10.0    46.4  24.8 80.7  14.0 4.7                               10    825      9.2     49.8  21.5 81.9  12.3 5.1                               30    750      9.0     33.3  33.6 72.8  20.2 6.1                               30    800      23.2    40.0  12.5 62.6  21.3 15.8                              30    825      23.5    39.6  10.0 61.1  21.1 17.4                              ______________________________________                                    

EXAMPLE 13

A gaseous feedstream consisting of 50 vol. % air in methane was contacted with silicon carbide at varying CH₄ GHSV and the results shown in Table 13 were obtained. The initial temperature of each run was 800° C.

                  TABLE 13                                                         ______________________________________                                         CH.sub.4 /Air Over SiC                                                         CH.sub.4                                                                       GHSV   % CH.sub.4                                                                              % Selectivity to:                                              (hr..sup.-1)                                                                          Conv.    C.sub.2 =                                                                              C.sub.2                                                                              C.sub.2 +                                                                            CO    CO.sub.2                             ______________________________________                                          600   10.6     30.0    14.1  48.3  40.0  11.6                                 1200   5.7      27.0    26.3  56.1  36.8  7.0                                  2400   2.6      19.2    38.5  57.7  34.6  7.7                                  ______________________________________                                    

EXAMPLE 14

A gaseous feedstream consisting of 50 vol. % air in methane was contacted with alpha-Al₂ O₃ at varying CH₄ GHSV and the results shown in Table 14 were obtained. The initial temperature of each run was 800° C.

                  TABLE 14                                                         ______________________________________                                         CH.sub.4 /Air over α-Al.sub.2 O.sub.3                                    CH.sub.4                                                                       GHSV   % CH.sub.4                                                                              % Selectivity to:                                              (hr..sup.-1)                                                                          Conv.    C.sub.2 =                                                                              C.sub.2                                                                              C.sub.2 +                                                                            CO    CO.sub.2                             ______________________________________                                          600   12.8     29.6    10.9  44.4  32.2  23.4                                 1200   6.5      29.4    23.2  55.7  30.3  13.9                                 2400   2.6      21.4    38.2  59.6  26.7  13.7                                 ______________________________________                                    

EXAMPLE 15

A gaseous feedstream consisting of varying amounts of air in methane was contacted with a solid consisting of 1.2 wt. % Li on alpha-Al₂ O₃ and the results shown in Table 15 were obtained.

                                      TABLE 15                                     __________________________________________________________________________     CH.sub.4 /Air over Li/α-Al.sub.2 O.sub.3                                 Vol %                                                                          Air     CH.sub.4                                                               in  Temp                                                                               GHSV                                                                               % Conv.                                                                               % Selectivity to:                                           CH.sub.4                                                                           (°C.)                                                                       (hr..sup.-1)                                                                       CH.sub.4                                                                          O.sub.2                                                                            C.sub.2 =                                                                          C.sub.2                                                                            C.sub.2 +                                                                          CO  CO.sub.2                                    __________________________________________________________________________     10  700 1200                                                                               0.1                                                                               8   0   77.5                                                                               77.5                                                                               0   22.5                                        10  800 1200                                                                               0.6                                                                               21  36.1                                                                               55.0                                                                               94.1                                                                               0   5.9                                         10  900 1200                                                                               2.9                                                                               88  54.1                                                                               9.6 93.0                                                                               0   7.0                                         30  700 1200                                                                               0.4                                                                               6   0   46.7                                                                               46.7                                                                               0   53.3                                        30  750 1200                                                                               1.0                                                                               14  19.7                                                                               50.2                                                                               70.9                                                                               0   29.1                                        30  800 1200                                                                               3.1                                                                               29  31.6                                                                               28.9                                                                               60.6                                                                               25.9                                                                               13.5                                        30  825 1200                                                                               5.1                                                                               44  34.3                                                                               18.8                                                                               57.8                                                                               32.0                                                                               10.2                                        30  900 1200                                                                               8.8                                                                               92  37.3                                                                               4.5 54.1                                                                               29.6                                                                               16.3                                        50  700 1200                                                                               0.7                                                                               5   0   30.1                                                                               30.1                                                                               0   69.9                                        50  750 1200                                                                               1.6                                                                               10  14.7                                                                               42.0                                                                               57.3                                                                               0   42.7                                        50  800 1200                                                                               6.5                                                                               25  25.2                                                                               21.9                                                                               49.7                                                                               36.5                                                                               13.8                                        50  825 1200                                                                               10.3                                                                              41  29.7                                                                               15.7                                                                               48.3                                                                               39.3                                                                               12.4                                        50  900 1200                                                                               17.6                                                                              90  29.4                                                                               1.8 34.2                                                                               43.6                                                                               22.2                                        50  800 2400                                                                               1.7                                                                               8   23.7                                                                               53.4                                                                               73.2                                                                               0   21.8                                        50  825 2400                                                                               3.7                                                                               14  27.0                                                                               33.9                                                                               62.5                                                                               26.4                                                                               11.1                                        50  900 2400                                                                               14.9                                                                              60  31.2                                                                               10.2                                                                               45.0                                                                               45.4                                                                               9.6                                         50  925 2400                                                                               17.9                                                                              76  29.0                                                                               6.7 39.8                                                                               47.9                                                                               12.4                                        __________________________________________________________________________

EXAMPLE 16

A gaseous feedstream consisting of varying amounts of air in methane was contacted with a solid consisting of 0.22 wt. % Li on TiO₂ (anatase) and the results shown in Table 16 were obtained.

                  TABLE 16                                                         ______________________________________                                         CH.sub.4 /Air Over Li/TiO.sub.2                                                Vol %                                                                          Air                                                                            in    Temp    CH.sub.4                                                                               % CH.sub.4                                                                           % Selectivity to:                                  CH.sub.4                                                                             (°C.)                                                                           GHSV    Conv. C.sub.2 =                                                                           C.sub.2                                                                             C.sub.2 +                                                                           CO   CO.sub.2                       ______________________________________                                         10    700     1200    0.29  10.7 82.9 92.7 0     7.3                           10    900     1200    3.7   42.7 9.1  73.7 12.2 14.1                           30    800     1200    8.4   37.1 21.7 63.5 20.3 16.3                           30    825     1200    10.9  37.3 17.4 60.2 21.1 18.7                           30    900     1200    9.5   36.5 4.4  51.4 28.0 20.6                           50    800     1200    12.9  30.6 16.5 50.2 31.2 18.7                           50    900     1200    20.6  31.9 5.4  43.3 32.1 24.6                           50    900     2400    20.5  37.1 10.1 51.5 28.0 20.5                           50    925     2400    21.6  37.8 10.1 54.3 22.6 22.7                           50    900     4800    16.2  39.1 14.8 58.2 30.7 11.3                           50    925     4800    18.1  39.3 12.9 56.4 31.2 12.3                           ______________________________________                                     

What is claimed is:
 1. A method for converting methane to higher hydrocarbon products and coproduct water which comprises contacting a gas comprising methane and a gaseous oxidant with silica at a temperature within the range of about 700° to 1200° C., said contacting being conducted in the substantial absence of reducible metal oxides.
 2. The method of claim 1 wherein the gaseous oxidant comprises molecular oxygen.
 3. The method of claim 1 wherein the gaseous oxidant comprises oxides of nitrogen.
 4. The method of claim 3 wherein the oxides of nitrogen comprise N₂ O.
 5. The method of claim 1 wherein the temperature is within the range of about 800° to 1000° C. 